What determines whether or not I get experience with each blow I land on a zombie?

Solution 1:

There are three different kinds of bonus experience in Dead Island.

The first is bonus experience from breaking limbs. This is possible via blunt weapons and fists.

The second is bonus experience from cutting limbs. This is possible via sharp weapons.

The third, and last, is bonus experience from head-stomping fallen zombies.

Additionally, this bonus experience is scaled based on the level of the zombie, and is also affected by some skills in the characters skill trees.